Pixologic has released a series of videos entitled “Helmet Design” in the free to use Zbrush Classroom. http://pixologic.com/zclassroom/homeroom/lesson/helmet-design-with-joseph-drust/
I have been through them all and find them extremely useful. Giving tips and insights into methods of hard surface creation and texture. Since the tutorials are based on a growing model, it allows the user to understand in a fundamental way different and alternative ways to accomplish results in Zbrush.
There are 37 videos, each average about ten to twenty minutes in length, so it may take a good few days to get through them. But it is well worth the study. I have been applying the methodology to my first hard surface sculpt in Zbrush, my bathroom sink.
Next step is texturing, then topology for the low poly, which will begin next week.
All the best